(WASHINGTON) — A “disturbing” attitude towards safety contributed to the track fire that killed one passenger and injured 91 more in Washington, D.C.’s metro system in January 2015, National Transportation Safety Board Chairman Christopher Hart said Tuesday.

Following an electrical arcing incident on the yellow line’s high-voltage third rail, hundreds of riders were trapped underground in a dark, smoky train for nearly an hour, many unable to pry open the doors.

As a voice on the loudspeaker urged passengers to “remain calm,” survivors say many were coughing, choking and crying.

Numerous issues — including an ineffectively deployed ventilation system and poor communication with first responders — intensified the situation, officials from the NTSB explained Tuesday.

A 61-year-old mother died of respiratory failure, and scores more suffered from smoke inhalation, authorities said.

According to the NTSB, the Washington Area Metro Transit Authority (WMATA) lacked comprehensive written procedures for responding to smoke and fire events in tunnels — and didn’t follow standard operating procedures where they had them.

For example, WMATA procedures dictate the control center stop all trains in both directions when smoke is reported in a tunnel. But disturbingly, according to the NTSB, rather than halting trains, “it was common practice to use trains with passengers to investigate reports of fire or smoke instead.”

“If WMATA had followed this standard operating procedure and stopped all trains at the first report of smoke, train 302 would not have been trapped in the smoke-filled tunnel,” investigators said Tuesday.

This isn’t the first time the NTSB has noted deficiencies in metro’s safety culture.

”Safety is still not institutionalized as a core value at WMATA,” Hart said Tuesday.

The NTSB’s criticism didn’t stop with the Metro. Officials also lambasted the “uniquely dysfunctional” tri-state oversight committee, and noted that the DC Fire Department and EMS had not practiced a full-scale tunnel evacuation for five years before the fatal accident at L’Enfant Plaza.